Ammonia is commonly manufactured by reacting synthesis gas (syngas) components nitrogen and hydrogen in an ammonia synthesis loop including a compressor, an ammonia synthesis reactor, ammonia condensation and recovery units, and purge gas recovery. After a pass through the ammonia synthesis reactor, the unreacted synthesis gas components are typically recovered and recycled to the compressor and the reactor in a loop. Make-up synthesis gas is continuously added to the ammonia synthesis loop to provide fresh hydrogen and nitrogen.
Synthesis gas typically contains inert components introduced with the make-up syngas, including argon, methane, carbon dioxide, and others, which do not contribute to ammonia production and undesirably accumulate in the loop.
Therefore, a purge gas stream is usually taken from the ammonia synthesis loop to avoid an excessive concentration of the inerts in the loop. The purge stream is typically processed in a hydrogen recovery unit, yielding a waste gas stream and a hydrogen-enriched stream for recycle to the ammonia synthesis loop. The waste gas stream comprises principally nitrogen with minor amounts of carbon dioxide, methane, hydrogen, and argon. In some cases, the waste gas can be used as a low heating value fuel gas.
A significant technological advance in the manufacture of ammonia has been the use of highly active synthesis catalysts comprising a platinum group metal such as ruthenium on a graphite-containing support, as described in U.S. Pat. Nos. 4,055,628, 4,122,040 and 4,163,775. Also, reactors have been designed to use this more active catalyst, such as a catalytic reactor bed disclosed in U.S. Pat. No. 5,250,270. Other ammonia synthesis reactors include those disclosed in U.S. Pat. Nos. 4,230,669, 4,696,799, and 4,735,780.
Ammonia synthesis schemes have also been developed based on the highly active synthesis catalyst. U.S. Pat. No. 4,568,530 discloses reacting a stoichiometrically hydrogen-lean synthesis gas in an ammonia synthesis reactor containing a highly active catalyst in the synthesis loop.
The present embodiments are detailed below with reference to the listed Figures.